The inner surface of a pneumatic tire is typically comprised of an elastomeric composition designed to prevent or retard the permeation of air and moisture into the carcass from the tire's inner air chamber. It is often referred to as an innerliner. Rubbers, such as halobutyl rubber and blends of butyl and halobutyl rubber, which are relatively impermeable to air are often used as a major proportion of the innerliners.
Accordingly, the air and moisture permeability resistance of the innerliner rubber composition is an important consideration.
The innerliner is normally prepared by conventional calendering or milling techniques to form a strip of uncured compounded rubber of appropriate width which is sometimes referred to as a gum strip. Typically, the gum strip is the first element of the tire applied to a tire building drum, over and around which the remainder of the tire is built. When the tire is cured, the innerliner becomes an integral, co-cured, part of the tire. Tire innerliners and their methods of preparation are well known to those having skill in such art.
There remains an ongoing desire to provide enhanced or suitable variations of butyl rubber-based tire innerliners without significantly affecting the air and moisture permeability resistance of the innerliner rubber composition.
In the description of the invention, the term “phr” relates to parts by weight of a particular ingredient per 100 parts by weight of rubber contained in a rubber composition. The terms “rubber” and “elastomer” are used interchangeably unless otherwise indicated, the terms “cure” and vulcanize” may be used interchangeably unless otherwise indicated and the terms “rubber composition” and “rubber compound” may be used interchangeably unless otherwise indicated. The term “butyl type rubber” is used herein to refer to butyl rubber (copolymer of isobutylene with a minor amount comprised of, for example about 1 to about 3 percent, of units derived from isoprene), and halobutyl rubber as chlorobutyl rubber and bromobutyl rubber (chlorinated and brominated butyl rubber, respectively) unless otherwise indicated. The term “partially depolymerized butyl rubber”, as used herein, is intended to be an ingredient other than an elastomer.
The term “Tm” relates to a melt point, or melting point, of a polymer, normally determined by a differential scanning calorimeter (DSC) with a temperature rise of from 3° C. to 10° C. per minute. The choice of temperature rise depends largely upon accuracy desired, with the 3° C. rise expected to be of greater accuracy, although a 10° C. temperature rise may often be used. The normal procedural aspect would be understood by one having skill in such art.